Slidable brake disc system

ABSTRACT

An axially, slidable brake disc system employs leaf springs between a hub of a suspension casting or knuckle to float the brake discs for axial sliding movement, while holding the discs against wobbling, and employs brake pads which are biased by springs to float on a stationary bridge so that the contact between the brake pads and discs is a light random contact thereby resulting in reduced residual torque drag and disc thickness variation. The rotating brake discs will shift axially, slightly from the braking position to the off-brake position with the brake pads urged by their spring forces to keep their pad faces parallel to and slightly spaced from adjacent brake disc surfaces to prevent corner engagement and localized rubbing contact thereby reducing pad wear, residual drag torque and disc thickness variation. The brake force applicator may be mounted at a 12:00 position and in an integral bore in the suspension knuckle to reduce the size, weight, and space envelope of the braking system. Less braking pressure is needed with two brake discs and four brake pads and the system will pass the AMS fade test.

[0001] This application is a continuation-in-part of PCT application,Application No. PCT/GB97/03388; filed Dec. 8, 1997, designating theUnited States and a continuation-in-part of PCT application, ApplicationNo. PCT/GB97/03386 filed Dec. 8, 1997, designating the United States.PCT applications PCT/GB97/03388 and PCT/GB97/03386 are herebyincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

[0002] This invention relates to a disc brake system and, moreparticularly, to a disc brake system for use on production vehicles.

[0003] Currently, production vehicles such as automobiles often havespot-type disc brakes, having a fixed brake disc and a caliperconfiguration with an inboard piston and cylinder operated by hydraulicfluid. The caliper is bolted to a suspension member either forward orrearward with respect to a vertical plane through a wheel axle andincludes a slidable bridge sliding on pins with an outer brake pad onthe outboard end of the bridge. Operation of the brake pedal forces thepiston outwardly to engage and to slide an inner brake pad along thebridge into frictional braking engagement with the inner side of thefixed disc, which is rigidly fixed to a hub on which the wheel ismounted. A reaction force on the slidable bridge causes it to slide onthe pins and force the outer brake pad tightly against the outer side ofthe fixed brake disc. Deceleration of the clamped disc and itsassociated hub and its attached wheel thereby decelerates the vehicle.As the piston is forced to slide to engage the brake pads with the fixeddisc, an internal O ring seal between the cylinder and the piston iscompressed, and energy is stored therein which is released, when thebraking fluid pressure is relieved, to slide the piston in the reversedirection to its off brake position in the cylinder.

[0004] This conventional disc brake hereinafter called a “conventional,fixed disc brake” because its brake disc is fixed to the wheel hub. Incontrast thereto, there is disclosed in the patent literature, such asU.S. Pat. Nos. 4,844,206 and 4,576,255; U.K. patent application 2 184801; and South African published application 70/5340, a pair of slidablebrake discs that slide axially along a wheel hub and utilize a fixedbridge with a fixed brake pad at a distal end of the bridge; and ahydraulic piston that slides the brake discs and slidable brake padsoutwardly to bring an outer side of the outer brake disc into brakingengagement with the distal, fixed brake pad. The fixed disc brake systemis widely used, particularly to brake the front wheels while theslidable brake disc system is not currently in use on productionvehicles. In order to be used on vehicles, any brake system must meet along list of demanding specifications, some of which are explainedherein. Until now, slidable brake disc systems appear to be unable tomeet the rigorous, demanding criteria to the satisfaction of automobilemanufacturers or suppliers. Vehicle manufacturers and brake suppliersundertake the risk of product liability lawsuits or product recalls and,therefore, are reluctant to adopt a new braking system unless it hassuperior qualities such as improved cost, weight, efficiency, longevityor other qualities relative to the standard fixed disc brake.

[0005] The current fixed brake disc systems used on vehicles are quiteheavy and a reduction in weight is a desirable goal for the slidabledisc brake system. In the fixed brake, the sliding bridge is quite largeand heavy as are the bolts to bolt the caliper unit to the suspensionmember and heavy slide pins are used to support the slidable bridge. Thetypical brake disc itself is also quite heavy with its bell or hat shapeand with its annular rim for engaging the brake pad.

[0006] Weight of the fixed brake disc system is detrimental not only tofuel efficiency but also to steering. That is, the brakes represent anunsprung mass on the wheel that must be turned and steered and that alsomust be supported to withstand high loads including the brake torque andloads due to a wheel going up and down as it travels over uneven roadsurfaces. The overall size of the fixed, disc brake and its location onthe vehicle suspension requires a large space envelope that limits thelocking angle and vehicle turning circle, particularly for some types ofwheel suspensions.

[0007] In addition to size, cost and weight, there are the criteria ofefficiency, proficiency and longevity. Brake wear is a longevity problemand a longer brake pad life and brake disc life are desired by vehiclemanufacturers which are increasingly providing long term servicewarranties for their vehicles, as well as for the vehicle owner whoultimately pays for brake replacement in one manner or the other. Thebrake disc life can be adversely affected by a localized, rubbingcontact between the brake pads and the brake pad, particularly at thebrake-off position of the braking system. If the brake disc is tiltedfrom a true, vertical plane normal to a horizontal axis through the hub,an increased localized rubbing contact of brake pads on the disc resultsand is a source of disc thickness variation (DTV), i.e., a differentthickness in cross-section of the fixed brake disc at different radiallocations from the disc axis. Significant DTV results in vibrations thatthe driver feels and requires costly brake maintenance to eliminate thevibration problem.

[0008] Some fixed disc brake systems have noise problems which are curedto a certain extent by the addition of noise suppressors, which add tothe size, weight and cost of the system. Brake systems must be free ofrattles and should be free of noise. The current bell or hat shape ofthe conventional fixed brakes can be noisy because an impact on the disccauses a noise resonance and loud sound due to its bell shape and fixedattachment to the hub. Therefore, it is desirable to eliminate such anoisy shape and fixed mounting of the brake disc to the hub.

[0009] In addition to above, there also may occur a “feel” problem wherethe driver experiences a long or deep pedal depression when operatingthe brakes. Sometimes the deep pedal is the result of “knock back” ofthe actuator piston in the cylinder in the piston return direction thatdisplaces hydraulic liquid and shifts the piston deeper in the cylinder.A cornering or bumps in the road may deflect the suspension or slidablebrake caliper and knock back the piston and cause the vehicle operatorto experience a deep pedal braking operation. Another potential sourceof “knock back” in the conventional sliding bridge, fixed brake discsystem is the result of an initial large deflection of the outer distalend of the slidable bridge at heavy braking loads where the bridgedistal end is often deflected 0.006 inch or more. The sliding bridgesare already quite heavy and massive to withstand the braking torque andto provide the stiffness for the distal end of the bridge. When thebrake pressure is released, the distal bridge end rebounds and can causeknock back of the piston in the cylinder.

[0010] Among the demanding temperature tests that vehicle brakes aresubjected to is the Auto Motive Sport (AMS) fade test in which the braketemperature is monitored during ten braking stops as fast as possibleover a very short time interval. In brief, the AMS vehicle test involvesthe driver flooring the gas pedal to accelerate vehicle extremely fastto 100 Kph. and then braking as hard as the driver can to stop thevehicle as quickly as it can be braked to a stop. This is quicklyiterated for a total of ten rapid accelerations and decelerations withthe temperatures of the brake disc being measured over the course of theten cycles. It is desired to keep the maximum temperature of the brakedisc below its “Judder” effect temperature at which severe disc geometryand metallurgical changes occur and deteriorate the brake disc. TheJudder effect temperature is usually in the range of 650° to 700° C.;and this AMS test is difficult to pass. In that AMS test of alightweight automobile having the fixed brake system (against which theslidable disc brake system of this invention is compared), the brakedisc temperature exceeded 650° C. and the temperature drop betweenbraking operations was only about 30° C. The test data described hereinis from two identical, production model automobiles of B Class frontwheel drive. They have a kerb weight of about 1000 Kgs. and a grossvehicle weight of about 1350 Kgs.

[0011] Manifestly, the test data for different vehicles may varysubstantially from that described herein, which data is given for thepurposes of illustration of one embodiment of the invention and is to beconstrued as a limitation for the invention as defined by the claimsattached hereto.

[0012] Brake disc temperature also can be monitored to provide anindication of “off-brake” residual torque of the braking system. Eventhough the vehicle operator is not operating the braking pedal and issteering the vehicle along a straight line path, the brake pads arerubbing against the fixed brake and causing the temperature thereof torise substantially above ambient. The cornering of a vehicle and sharpturning may also shift the slidable brake caliper into rubbing contactwith the fixed brake disc. In a current production vehicle oflightweight and having a fixed brake system, the disc temperature wasmeasured at least 35° C. above ambient when the ambient temperature isbetween 10° to 20° C. This is a good indication that current fixed brakesystems have considerable residual torque at the off-brake condition,and concomitant wear and fuel energy waste. It will be recognized thatthe bell or hat shape of fixed brake disc has non-uniformcross-sectional thickness at the corners and has different fillets thatcan result in non-uniform expansion thereby causing an increase in thespace envelope of the outer rim of the brake disc and resultant rubbing,thereby producing a high off-brake, residual torque.

[0013] In order to test conventional brakes when used in mountainousterrain having descending, steep grades with much cornering of thevehicle, a conventional disc brake was tested over thirty descents of asteep mountain with each descent lasting about twenty-four minutes.These fixed brakes discs on a lightweight, production car experiencedtemperature of over 600° C. after about 13 minutes of descent; and theyreached a maximum temperature of almost 680° C. at the end of the run.Hence, there is a need for a disc brake system that runs cooler in sucha test so that it does not potentially cause a Judder effectdeterioration of the brake disc in mountainous usage. These fixed discbrakes had high brake fluid temperatures and poor standing soakingcurves after trans-mountain runs.

[0014] It will be appreciated that in sliding brake disc system thatbrake disc must slide axially on the hub between an off-brake position,where the residual torque should be low and a braking position where thetorque is high, and then return to the off-brake position to reduce theresidual torque. The sliding connection between the brake disc and hubmust be free to move despite being subjected to corrosive conditions andover a long period of use. The slidable brake disc must not be noisy orsqueal under low and high temperature conditions, and it must not wobbleor generate dust or produce vibrations that the driver can feel or hear.In the patent literature, such as U.K. patent application 2 184 802 andU.S. Pat. No. 4,576,255, the slidable brake disc systems had splinegrooves oversized relative to the size of the disc teeth inserted intothe grooves and spring devices where mounted on the hub to push thediscs to rotate a driving side, flank of each tooth into matingengagement with a flank of the oversized spline groove. The oversizednotches were used to prevent the previously heated and now cooled discfrom jamming in the splines. To eliminate “knock back” and chattering,springs were inserted into the spline notches to bias the spline flankson the disc and hub into engagement with one another. Such designs donot provide a good drive connection between the discs and the splinedhub, are costly and apparently allow the discs to wobble relative to thehub at high braking loads.

[0015] From the foregoing, it will be seen that there is a need for abetter, slidable disc mounting system that is more efficient and thatdoes not generate noise or squeal as the brake discs expand at hightemperatures and that does not wobble at high braking loads. Also, thereis a need for a twin disc braking system that operates at low residualtorque in an off-brake condition to reduce DTV and energy loss.

SUMMARY OF THE INVENTION

[0016] In accordance with the present invention there is provided a newand improved slidable disc brake system particularly adapted for use onproduction vehicles. This is achieved by the use of a unique mountingand control of the positions of the slidable brake discs and brake padsthat results in low frictional face pad wear and a low, off-brake,residual torque and a good drive connection between the hub and theslidable brake disc.

[0017] The preferred construction uses force applicators such as leafsprings located between the hub and the brake discs to float the brakediscs for axial sliding movement and to hold them against wobbling onthe hub while allowing the brake discs to have light, random contactwith the brake pads. The rotating brake discs will shift slightly in theaxial direction on the hub from their brakes-on position to establish abrakes-off position. These rotating, floating discs also exert axiallydirected forces on the brake pads to slide them axially to theiroff-brake positions along the stationary bridge. The brake pads areconstrained by force applicators such as leaf springs to keep their padfaces parallel to the brake discs and not to allow the brake pad facesto tilt into a corner engagement with the brake disc as would causelocalized rubbing contact, thereby generating disc thickness variationin the brake discs and resultant vibration of the discs. That is, thespring holds the brake pad against tilting movements and axial slidingmovements on the supporting bridge by vibration and inertia forcescaused by operation of the vehicle. If allowed to tilt on the bridge,the pad faces experience a localized rubbing contact which increases theresidual drag torque, pad wear and DTV at the off-brake position. Thebrake pads are preferably constrained by leaf springs to float on thebridge and the brake pads are constrained by leaf springs between thediscs and hub to float on the hub so that the contact between the brakepads and discs is a light, random contact thereby resulting in reducedresidual drag torque and disc thickness variation.

[0018] Preferably, the respective leaf spring forces applied to brakepads and the brake discs are balanced relative to one another so thatthe system can move from its braking condition to its off-brake positionby action of separation forces between the discs and the braking pads;and yet, the brake pads are held in the off-brake position againsttilting under vibration and vehicle caused inertial forces and therebycausing a localized rubbing and DTV. More specifically, in the case of atwo-brake disc system, when shifting from the brakes on-condition tobrakes off-condition, the outer brake disc slides axially on the hub toseparate itself from the stationary, distal brake pad fixed to thebridge; and the central slidable brake pad between the first disc andthe second disc slides axially along the bridge away from the first discto separate its outer pad face from the facing side of the first disc.The second, inner brake slides axially along the hub toward the pistonand cylinder assembly to separate itself from the inner pad face on thecentral brake pad. The inner slidable brake pad at the piston slidesaxially inward toward the piston and cylinder assembly to separate itsouter friction face from a facing side of the second brake disc. Therespective leaf springs on the bridge and on the hub are balanced toallow this separation and yet hold the brake pads and brake discs fromtilting, as would cause DTV or from unwanted axial sliding engagement aswould cause a high residual drag torque, under the vibration and vehicleinertial forces being experienced by an unsprung brake system.

[0019] The floating twin disc, slidable brake discs and floating brakepads of the present invention provide a brake system that passed the AMSfade test with temperatures significantly lower than the conventionaldisc brake tested which did not pass this test. These twin disc brakeshad a maximum temperature of about 120° C. lower than the maximumtemperature for the fixed brake which was in the Judder range. Also, thecooling of the twin disc brakes was about 80° C. between stops relativeto a cooling of about only 30° C. between stops for the standard fixedbrake. Also, very significant results were found in the temperature ofthe fixed brake disc and the slidable brake discs as the respectivebrake discs cooled after braking at 100 mph with the fixed braketemperature above ambient being at 3.5 times higher than slidable braketemperature above ambient. This shows that the twin disc, slidable brakehas significantly lower drag torque. An objective of the invention is toreduce the drag torque to about 1 newton meter as compared with a tested6.0 newton meter as compared to a conventional disc brake tested. Thus,the slidable, twin disc brake system of this invention was found to haveimproved operating characteristics relative to operating temperatureswhen compared to a standard, fixed disc brake system.

[0020] In the preferred embodiment of the invention described herein, asignificant size and weight reduction are achieved relative with thetwin slidable brake system of this invention relative to a conventionalfixed disc brake system with its large sliding caliper. Morespecifically, an unsprung, weight reduction in excess of 2 Kgs. wasachieved for each front wheel. This is a very significant weightreduction and has implications for fuel savings, suspension design,vacuum assists, steerability, etc. This weight saving of 2 Kgs. isrelative to a lighter, solid, fixed brake disc; and relative to aheavier, ventilated fixed brake disc, the average saving may be as muchas 3.6 Kgs. per front wheel. This is an unsprung weight reduction whichis desired by production vehicle manufacturers.

[0021] In accordance with an important aspect of the invention, thebrake cylinder is integrally formed in the suspension casting or knuckleabove the axle on the vertical centerline. This integral suspensioncasting reduces the number of parts for the suspension and provides amore compact, and lighter weight system. The floating brake disc systemdoes not knock back the piston during cornering or other dynamicmovements as easily as the large sliding caliper standard disc brake.Also, the fixed bridge need not be large and heavy as the slidingcaliper bridge which, even though large and heavy, deflectssignificantly under heavy braking loads by 0.006 inch, for example.These large sliding caliper disc brakes are usually mounted at about3:00 o'clock or 9:00 o'clock positions rather than a preferred 12:00o'clock position for the twin slidable disc brake of this invention.Also, the mounting of the bridge above the axle at the verticalcenterline position allows an increase in steering angles and vehicleturning circle.

[0022] The unit cost reduction for the embodiment of the inventionillustrated herein relative to a current fixed brake system for the samevehicle is estimated to be substantial and may approach 35% for the samevehicle. The slidable twin disc brake of this invention is designed topursue the goals of substantial reduction in cost, weight, spaceenvelope; increased longevity of brake pads; and better efficiency inmanufacture, assembly and performance.

[0023] When the slidable disc brake is used with two slidable brakediscs and four brake pads, such as on the front wheels of a productionvehicle, the braking pressure needed may be about 50% of the brakingpressure used today with the conventional systems using a fixed disc andtwo braking pads. Higher braking pressures applied to the brake discusually can result in higher disc temperatures. The requirement for highbrake pressures has resulted in the large-scale use of braking assists,such as vacuum assists and, in large commercial diesel trucks, the useof vacuum pumps to supply the vacuum for the brake assist system. Thevacuum assists add weight and cost to the vehicle. The reduced brakingpressure of this invention allows elimination of a vacuum assist system,in some instances, or the use of a smaller assist to generate thereduced brake pressure used in the slidable disc brake.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a perspective view of a slidable, twin disc brakeassembly constructed in accordance with a preferred embodiment of theinvention;

[0025]FIG. 2 is a diagrammatic view of an outer spring constraining thebrake pads and an inner spring constraining the brake discs;

[0026]FIG. 3 is a plan view showing the spring constraining the brakepads;

[0027]FIG. 3A is a cross-sectional view showing the spring applyingrestraining forces to the tops of the brake pad carriers;

[0028]FIG. 4 is a diagrammatic view of three leaf spring constraining abrake disc on a hub;

[0029]FIG. 5 is an exploded view of the illustrative assembly;

[0030]FIG. 6 is a side elevational view of the illustrative assembly;

[0031]FIG. 7 is similar to FIG. 6 but shows the illustrative assembly invertical cross section;

[0032]FIG. 8 shows temperature decay curves for disc brakes due toresidual drag torque with the brakes off;

[0033]FIG. 9 shows curves for an AMS fade test of a standard fixedbrake;

[0034]FIG. 10 shows the curves for an AMS fade test of a twin discbrake;

[0035]FIG. 11 is a vertical cross-sectional view taken through asuspension link of the illustrative assembly;

[0036]FIG. 12 is a view similar to FIG. 16, but of a modification of theillustrative assembly;

[0037]FIG. 13 is a perspective view of an alternative leaf spring havingraised ribs thereon;

[0038]FIG. 14 is a diagrammatic, enlarged view of the points of contactbetween the leaf springs and the brake disc;

[0039]FIG. 15 is an enlarged, fragmentary and exploded view of thedriving connection between a hub and slidable brake disc;

[0040]FIG. 15A is similar to FIG. 15 except that the driving connectionis enlarged and meshed to drive the brake disc with rotation of the hub;

[0041]FIG. 16 is a view taken in the direction of the arrow XVI in FIG.6;

[0042]FIG. 17 is a view taken in the direction of the arrow XVII in FIG.7; and

[0043]FIG. 18 is a fragmentary view of a sealing ring engaging a pistonin a hydraulic cylinder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0044] As shown in the drawings for purposes of illustration, theinvention is embodied in a slidable disc brake assembly 10 which canhave either one slidable braking disc 38 or two or more slidable brakingdiscs such as a pair of brake discs 38 and 40 (FIGS. 1 and 2)illustrated herein for a front wheel drive car. In a front wheel driveautomobile suspension and wheel assembly, as illustrated and describedherein, the weight of the vehicle is concentrated at the front of thevehicle and more brake torque is applied to the front wheels than isapplied to the rear wheels. It is contemplated that the rear wheel brakeassembly will have only the single slidable disc; and a single pair ofbrake pads 50 and 60, while the front wheel brake assembly will have thesecond slidable disc 40 and additional brake pads 54 and 56 on aslidable, intermediate pad carrier 58. The present invention is directedto and claims a slidable disc brake system that can have one, two ormore slidable discs and that can be used in other applications thanautomobiles.

[0045] Conventional disc brakes or production vehicles have a single,fixed brake disc (not illustrated) and a single pair of brake disc padsand this requires considerable pressure, such as 70 BAR, to be appliedbetween the pads and the fixed disc to generate the required brakingtorque. This higher pressure requirement has resulted in the use ofbraking assists, such as a vacuum assist or a vacuum pump, to generatesufficient braking force. This adds cost and weight to the vehicle andnecessitates higher pressure in the brake conduits and stronger and moreexpensive brake fluid lines to handle the high pressure. The use of thesecond slidable disc and a second pair of brake pads with a doubling ofthe engaged brake surfaces provides a braking assembly that works at 50%of the conventional pressure, e.g., 35 BAR. Higher pressure causes morewear and higher temperatures, and it is desirable to reduce pressuresfor these reasons alone. Thus, the second slidable disc enables thebraking torque to be shared among four (4) engaged, friction surfacesinstead of the conventional two—thereby reducing pressure, heatgeneration and wear.

[0046] As disclosed in the patent literature, there is a problem ofrattling and noise generation encountered between the slidable brakediscs and the supporting hub on which they slide. As described above,the discs may be heated to 300° C. to 600° C. when being subjected toextreme braking conditions such as cornering and braking down a mountainor when being subjected to the fast and repetitive braking and/orcornering as in the AMS test. These prior slidable twin disc systemswere equipped with various spring devices mounted on the hub to push thediscs to rotate and to abut a driving side flank of a disc spline toothagainst an adjacent, mating flank driving slide flanks of a hub splinegroove. The spline grooves in the hub were oversized relative to thesize of disc teeth to prevent binding of the spline teeth in the splinegrooves, and these oversized grooves allowed the discs to wobble at highbraking pressures, as described in the aforesaid patent literature. Whenthe braking pressure is released, the South African patent describes theuse of release springs to push the brake disc axially along the hub.Axial directed spring pressures on the brake discs will increase thefrictional off-brake, residual torque and should be avoided for thisreason. It is a considerable problem to stabilize the slidable brakedisc and yet allow the brake disc to slide freely at temperatureextremes where the brake and the ambient temperatures are very low orvery high after a considerable expansion of the disc particularly at itsslidable driving connection to the colder hub. Also, the twin disc brakeshould have a lower off-brake, residual torque than that of theconventional fixed disc brake. Also, as explained above, for successfuladoption by the automotive industry, the slidable twin disc brakesshould meet the goals of a substantial reduction in cost, weight, spaceenvelope; increased longevity of brake pads, and efficiency inmanufacture, assembly and performance.

[0047] In accordance with the present invention, there is provided aslidable disc brake assembly having one or more brake discs 38, 40 whichare mounted on a hub 14 of a suspension for a vehicle with the brakingdisc being constrained i.e., positioned on the hub 14, along its innerradial portion by a resilient radially directed force applicator 44acting between the hub 14 and the brake disc and by an outer forceapplicator assembly 45 which is positioned at the outer rim of the disc.This construction provides a rotational geometry for the disc to havecontact between the disc and the brake pads in a random nature, therebyresulting in a lower residual, off-brake torque and reduction of DTV.That is, a gentle random touching of the brake pads and brake disc mayoccur when driving straight ahead with the pads and disc being held innon-tilting positions relative to one another. The inner, radiallydirected, force applicator is positioned between the slidable disc, andthe hub to provide friction forces to the hub and to the disc whichholds them against sliding relative to one another and againstgenerating a noise or a high squeal when the brake disc is heated andexpanded. That is, when the brake disc was cold, no squeal or noise wasgenerated at the spline interconnection. But, when the disc was heatedand expanded, disc spline members or teeth 42 (FIG. 5) were loose andslid in hub splines 20 and generated high pitched squealing noises.

[0048] As will be explained in greater detail, the preferred radial,inner force applicator 44 comprises springs, preferably flat leafsprings 44 a, that are laid tangentially of the hub at their centers 44b (FIGS. 4 and 5) and with their outer ends 44 c biased into contactwith inner hub surfaces at spaced points, as illustrated in exaggeratedform in FIG. 4. More spaced points of contact can be provided byproviding raised ribs 44 d on the leaf springs 44 x, as illustrated inFIGS. 13 and 14.

[0049] The slidable brake disc 38 is thus supported in a floating manneron points of contact 44 c (FIG. 4) with the leaf springs 44 a on the hubin a floating manner and the brake disc can be shifted axially withforces applied thereto to overcome the frictional forces being appliedby the springs at inner disc hub surface. When the brake disc expandsconsiderably due to a disc high temperature, the disc teeth become loosein the colder spline hubs and the frictional forces between the leafsprings 44 a and the brake disc and hub restrain the disc from shiftingrelative to the hub and a resultant squealing noise. The leaf springs 44a impart radially directed forces to the inner hub portion of the brakedisc to keep it generally in a plane normal to its rotational axisthrough the center of the hub. This inner radial positioning by thesprings 44 a assists in keeping the disc 38 concentric with therotational axis and within a relatively tight space envelope at thebrakes off condition thereby reducing rubbing contact between the brakepad's frictional surfaces and the brake discs 38, 40 and a resultantdisc thickness variation (DTV). DTV which is a major source ofvibration.

[0050] In accordance with an important aspect of the invention, slidablebrake discs 38 and 40 float on the hub 14 and its outer rim portion isconstrained to its off-brake position, and each disc seeks or floats toan off-brake position established by engagement with slidable brake pads50, 54 and 56, which slide on the guide surfaces 68 of the bridge-shapedguide member 64. As best seen in FIGS. 2, 3 and 3A, a brake pad, forceapplicator 71 is positioned to apply radially directed loads to theslidable brake pads to constrain them from sliding with predeterminedspring forces. The spring forces are much stronger than that neededmerely to prevent rattling or noise suppression. The spring forces aresufficient to restrain the slidable brake pads from moving into contactwith the brake discs in an uncontrolled manner. It has been found thatif only a light spring force is supplied to suppress noise, that thenoise will be abated; but that the brake pads are free to shift and rubagainst the brake discs causing wear and DTV. Also, when using verylight springs, the brake pads will not assist in positioning the outerrims of the slidable brake discs to reduce off-brake residual torque.The illustrated force applicator 71 comprises a pair of leaf springs 71a and 71 b (FIGS. 2 and 5) which form the dual functions of preventingrattle and positioning of the pads and discs relative to each other.

[0051] After the brake has been applied and released, the rotating brakedisc 38 initially rubs against the brake pads and forces from thisrubbing cause the disc pads 50 and 56 to slide in opposite directionsfrom the rotating disc. The amount of shifting is controlled by thebrake force applicator's frictional force being overcome. Conversely,the off-brake, residual torque position of the rotating brake disc 38 isbeing constrained by the forced-apart brake pads, which are being heldagainst further sliding by the force applicators. The force applicatorsprings 44 also are controlling any lateral sliding of the brake disc 38along the hub. The brake disc 38 is being constrained in its off-loadposition by the outer force applicators acting on opposite sides of thepair of discs and the inner springs 44 acting on the inner hub portionof the discs. Thus, the disc is controlled to be free to slide and floatbut not to topple into the brake pads and the brake pads have controlledsliding but are not free to topple or to be free to vibrate into or bangagainst the discs.

[0052] The twin disc brake assembly 10 of the present invention, becauseof its floating geometry as described above, has a significantly lowerdrag torque, i.e., off-brake residual torque, as will be explained inconnection with FIG. 8 which illustrates a typical result for the disctemperature curves from 100 Kph. for a slidable, twin disc brake versusa conventional, fixed disc brake. The conventional fixed brake curves13A plateaus at best is 35° C. above ambient while the slidable, twindisc brake 10 continues to cool and stabilizes at 10° above ambient, asillustrated by the straight line 13B. Usually, the conventional brakewas found to be about 50°-70° C. above ambient. The assumption made withrespect to this test is that dynamic drag due to disc face contact withthe pad is proportional to temperature at the disc. The presentinvention is designed to preferably produce a low residual torque, e.g.,about 1 newton meter or less in contrast to about 6 newton meter for thefixed disc brake on the vehicle being tested herein.

[0053] In accordance with the invention, the brake discs 38 and 40 mustbe flat and planar in their rotational plane and substantially normal tothe rotational axis 9 (FIG. 2). The brake disc pads have outer planarsurfaces 50 a, 54 a; 56 a and 60 a which are held by the springs 71 aand 71 b to be parallel to the disc annular braking surfaces 38 a and 40a at the outer rim portion of the brake discs 38 and 40. When the discgeometry is slightly curved, i.e., not a flat planar surface, it hasbeen found that localized rubbing and wear occurred, as illustrated inFIG. 2, at a lower corner 50 b of the cylinder brake pads 50 and at theupper outer corner 54 b of the opposed brake pad 54 on the slidable padcarrier 58. FIG. 2 shows a very exaggerated tilted disc 38 in lines toillustrate the point being made. The non-flat brake disc did not haverandom contact with the brake discs 38 and 40; but had localized rubbingcontact due to the disc curvature at the inner and outer corners 50 band 54 b during each or almost each revolution of the brake disc. Severedisc thickness variations resulted and vibrations of the brake occurred.When the non-flat discs were replaced with flat brake discs the randomengagement of the pads and discs was again achieved, the DTV andvibrations associated with the DTV were eliminated. If a localized spotcarries the load, you get wear and a pumping action at wheel frequency.

[0054] While not illustrated herein, it was found that if the slidablebrake pad surfaces 50 a, 54 a, and 56 a (FIG. 2) were not held inparallel relationship to the brake disc faces 38 a and 40 a, but werefreely mounted or loosely mounted on the bridge, that the brake padscould tilt or cock and cause DTV and resultant vibration, as describedabove for a non-flat brake disc. Stated differently, the springs 71 aand 71 b were strong enough to hold the brake pads against a tiltingthat would shift their planar pad surfaces 50 a, 54 a and 56 a fromplanes perpendicular to the rotational axis 9 and would bring a cornerthereof into continual, localized rubbing contact with a brake disc inthe off-brake position. Thus, the floating geometry for the brake discsand constraint of the brake pads and discs to achieve random contact atthe off-brake position is an important aspect of the invention.

[0055] AMS fade tests were run to compare the performance of a slidable,twin disc brake assembly 10 versus the standard factory equipped fixedbrake disc, and the results are shown in FIGS. 9 and 10. As seen in FIG.9, there are ten peaks on the graph for each of the ten braking stopswith the brakes cooling and showing a temperature drop of about 30° C.and a maximum disc temperature of about 700° C. which is the Judderrange. In contrast, the twin slidable brake disc system had a maximumtemperature of 580° C. (FIG. 10) or about 120° C. lower than theconventional disc brake. The temperature drop between braking events wasabout 80° C. compared to only a 30° C. temperature drop for conventionaldisc brake. Thus, the present invention passed the AMS fade test wherethe conventional brake being tested did not pass the AMS test.

[0056] In accordance with the present invention, the preferred driveconnection 19 has the brake disc teeth 42 sized to fit the grooves 20along both of the groove flanks 21 without using oversized grooves. Thisis in contrast to the prior art which used oversized spline grooves andsmall springs therein to engage the driving side flanks of the hub anddisc; but this prior art solution led to other problems like disc wobbleon the hub. Preferably, the driving connection of the present inventionis a very efficient one such as that akin to a pair of meshed gearswhere the contact is a line of contact across the engaged flanks 21(FIG. 15A) rather than a small point of contact to provide lower unitpressures. Preferably, this line of contact is maintained whether thebrake disc has a high or low temperature. The plastic deformation at theengaged spline surfaces keeps the engaged spline members clean fromcorrosion. The present invention eliminates the brinneling, dustgeneration, and squirming of the disc at high braking torque.

[0057] The hub 14 is an integral casting and, as is conventional, has ahollow cylindrical rearward projection 14 a which has a splinedinterior, and an exterior, which provides a mounting for roller bearings16 (FIG. 7). A splined projection of a constant velocity joint (notshown) at the end of a drive shaft is received within the projection sothat the hub can be rotated on the bearings 16 by the drive shaft. Thehub also has an annular disc-like portion 14 b from which the portionprojects rearwardly. The hub provides a mounting for the wheel (notshown) which is bolted against a forward surface of the portion by boltsreceived in holes 14 d. The hub also has a hollow cylindrical rearwardprojection 14 c of greater diameter than the portion. The portionprojects from the outer edge of the portion 14 b. The portion 14 c hasan outer surface provided with grooves 20 running parallel to the axis22 about which the hub rotates. The grooves 20 are arranged in fourequally circumferentially-spaced locations.

[0058] The suspension link 12 (FIG. 11) is an integral casting andcomprises a hollow cylindrical portion 12 a of conventional form, whichprovides a mounting for the bearings 16 so that the hub 14 rotates onthe link. The link also comprises top 24 and bottom 26 mountings forsupports of the link. The top mounting is provided by a portion 12 b ofthe link which projects rearwardly from a portion 12 c which projectsupwardly from the portion 12 a. The portion 12 b is of conventional formand forms two semi-cylindrical arms (FIG. 5) which together form a clampwhich can be tightened by a bolt (not shown) which extends through bores28 in the arms and across a gap between them. A McPherson strut (notshown) can be clamped between the arms of the portion 12 b so that thelink can pivot about the longitudinal axis of the strut.

[0059] The bottom mounting 26 is provided by a portion 12 d of the link12, which projects downwardly from the portion 12 a thereof. Thisportion 12 d is of conventional form and has a vertical bore 30, toreceive a pin of a ball joint (not shown), and two horizontal bores 32in which bolts (not shown) can be received to connect the link to a tiebar (not shown).

[0060] The link 12 also comprises an arm 34 for connection to a trackrod (not shown) of a steering system of the vehicle. This arm 34 is ofconventional form and is provided by a portion 12 e of the link 12,which projects sideways from the portion 12 a thereof. The arm 34comprises a vertical bore 36 through which the arm can be pivotallyconnected to the track rod. In order to steer the vehicle, the track rodis moved to cause the link to pivot on the joint 18 and the mountings 24and 26.

[0061] The illustrative assembly 10 also comprises the two brake discs38 and 40, which are mounted for rotation with the hub 14. The two discsare identical to one another and are mounted for limited movement on thehub 14 in a direction generally parallel to the axis 22 about which thehub rotates. Specifically, each disc is in the form of a flat annularplate and has inwardly-projecting teeth 42. As best seen in FIGS. 5, 15and 15A, it is preferred that the brake discs 38 and 40 each have alimited number of wide teeth, i.e., the illustrated four teeth 42 thatmesh with the spline grooves 20 a of splines 20 on the hub. The splinegrooves 20 a are four in number, in this instance, and have flankingwalls 21 (FIG. 15) that match flanking walls 42 a on brake disc teeth42. The engaged flanks 21 and 42 a have an angle A for their respectivetooth flange angles. Manifestly, the number of teeth and splines may bevaried. Because of large stresses generated on the thin teeth 42 onthese relatively thin brake discs, there is a tendency of stress cracksto form, particularly after high temperature heating and cooling cyclesand high stress cycles. To relieve such stress, there are providedlarge, curved, stress relief fillets or cut-outs 42 b in the respectivebrake discs. Herein, as shown in FIGS. 15 and 15A, the stress relievingfillets are provided on each side of a tooth 42 and provide generallysemi-cylindrical, cross-sectional openings on each side of each tooth,when the teeth are fitted into a spline grooves, as shown in FIG. 15A.

[0062] As best seen in FIG. 5, the four grooves 20 on the hub arerelatively small compared to the projecting teeth 20 b defined betweeneach pair of adjacent grooves 20. These teeth 20 b on the hub havelarge, arcuate surfaces 20 c against which are laid the leaf springs 44.Thus, each leaf spring 44 has a large circumferential area contact withinner, arcuate surfaces 42 c of the brake disc in the place betweendepending teeth 42 thereon.

[0063] Four leaf springs 44 are mounted on the hub 14 to provideresilient force applying means to apply radial forces between the huband the discs 38 and 40. These radial forces prevent the discs fromtilting on the hub, prevent rattling and control sliding of the discsalong the hub. The resilience of the springs allows thermal expansion tobe accommodated, as explained above. The springs are secured in asuitable manner, such as by screws 46 to the outer surface 20 c of thehub portion 14 c in the gaps between the spline grooves 20 a. Each ofthe four springs engages both of the discs 38 and 40 in the areasbetween the teeth 42, giving a resilient four-point mounting for eachdisc. The discs can slide on the hub parallel to the axis 22 with theteeth sliding in the spline grooves 20 a.

[0064] As best seen in FIG. 4, the flat leaf spring 44 is engaged withand has a pressure line of contact with the hub at point 44 b; and theouter ends of the spring 44 c have been flexed downwardly to providepressure line of contact engagement with the discs 38 and 40 at thesebent spring ends. Only three springs 44 are shown in the diagrammaticillustration of FIG. 4 to illustrate the flexing of the springs 44;while in the embodiment of the invention described and illustrated inFIG. 5, four springs are used. In order to provide more lines ofengagement between the disc and the hub, the spring 44 x may be providedwith ribs 44 d therein, as shown in FIGS. 13 and 14. Also, it ispreferred to separate the spring 44 into separate biasing portions 44 hand 44 i (FIG. 13) separated by a slot 44 j each portion acting on anassociated disc 38 or 40 to provide more individualized, independentpressure forces between the associated disc and the hub. The springs 44are balanced in the force they apply to the brake discs 38 and 40relative to the force which the springs 71 a and 71 b apply to theslidable brake pad carriers 52 and 58. Both the brake discs and thebrake carriers are constrained against shifting along the hub and thebridge respectively, due to vibrations and inertial forces from thevehicle when it is traveling. Thus, it will be seen that the springs 44allow the slidable brake discs to: float on the hub, hold the discs in aradial plane normal to the rotational axis, apply frictional forces thatprevent squealing; apply frictional forces that aid in holding the discsin position while rotating in their off-brake positions; and permitaxial forces from the force actuator to outwardly slide the discs totheir braking position with engagement of the disc 40 with thestationary brake pad 60.

[0065] The illustrative assembly 10 also comprises the friction materialpads arranged on opposite sides of each of the discs 38 and 40. Thesepads comprise the first pad 50 which is mounted on a backing plate 52and is arranged to engage a side surface of the disc 38, pads 54 and 56,which are mounted on opposite sides of a backing plate 58 and arearranged, respectively, to engage the opposite side surface of the disc38 and a facing side surface of the disc 40, and the pad 60 which ismounted on a backing plate 62 and is arranged to engage the oppositeside surface of the disc 40. The backing plate is fixedly mounted on aguide member or bridge 64, which is, in turn, fixedly mounted on theportion 12 c of the link 12. Specifically, two bolts 66 pass throughbores through the portion 12 c and the guide member 64, and havethreaded ends which are received in threaded bores in the backing plate.The stationary guide member 64 provides two guidance surfaces 68 onwhich the backing plates 52 and 58 slide. The guidance surfaces 68extend, parallel to the axis 22, along opposite sides of the member 64.The guidance surfaces may take other forms such as the shafts of thebolts 66.

[0066] Each guidance surface 68 receives a pair of concave, U-shapedprojection or hooks of the pad carriers 52 and 58. As best seen in FIG.3A, the slidable pad carrier 58 has hook-shaped projections 59 withinner sliding surfaces 59 a, which are slidably supported on theupwardly-facing support surfaces 68 of the bridge 64. To assist inachieving the desired balance to allow the brake pad carriers 52 and 58to be pushed apart from and by the brake discs 38 and 40, when they areshifting axially from their brakes-on to their brakes-off positions; andyet constrain the pad carriers and their brake pads from tilting, it ispreferred to machine flat the inner sliding surfaces 59 a on thecarriers and the supporting surfaces 68 on the bridge. Flat machinedsurfaces on the carriers engaging flat machine surfaces on the bridgeassures a more uniform, frictional, constraining force to retain thebrake pad carriers against axial sliding from their off-brake positions.Also, the carriers will have broader, wider engagement with bridgesupporting surfaces 68 to assist in preventing significant rocking ortilting on the bridge under vehicle inertial forces and/or vibrationswhen the vehicle is moving, as would cause localized rubbing contact inthe off-brake condition.

[0067] If the slidable brake pad position is not controlled, theslidable brake pad may tilt to engage or to vibrate against the slidablebrake disc and generate a random wear pattern on the disc causing DTVand vibration of the disc. The control of the slidable pad and disc isimportant in a very dynamic situation with the vehicle wheel carryingthe slidable brake system over bumpy or smooth roads, cornering withbrakes on, cornering with brakes off, with ABS system on, with an ABSsystem off, etc. On cornering, the hub deflects and moves the discsurface to engage the brake pad; and after cornering, the pad and discseparate as the brake recovers to its steady state of low residualtorque at the off-brake position. In the embodiment of the invention,illustrated in FIGS. 2, 3 and 3A, the preferred force applicatorscomprise flat leaf springs 71 a and 71 b that have been bent from theirflat planar condition to a bow configuration in which outer edges 71 cand 71 d of the springs abut top end surfaces 52 a, 52 b, 58 a, 58 b ofthe respective slidable brake carriers 52 and 58. The center portion ofthe leaf spring 71 a is secured by a suitable fastener, such as screws69 threaded through the spring and into the stationary bridge 64 at acentral location on the top of the stationary bridge 64.

[0068] The force applicator 71 may take many forms, and it is hereinillustrated in FIG. 3 as having the two separate leaf spring portions 71a and 71 b, each of which is separately applied resilient, biasingforces to its associated brake pad holder 52 or 58. The leaf springportions 71 a and 71 b are preferably connected by a short integral,central web 71 f, which is located between a pair of facing, elongatedslots 77 dividing the spring leaf into the two discrete spring forceapplicator sections. Thus, if one brake pad holder has high pointsthereon or other force mitigating or amplifying factors affecting it andits associated spring; the other brake pad holder and its associatedspring should be isolated therefrom.

[0069] In the illustrated embodiment of the invention, the brakeactuating force used to brake the vehicle is from a brake actuator whichis in the form of a hydraulic piston and cylinder assembly 75, althoughit is contemplated that the actuating force could be from a brake bywire actuator. In a brake-by-wire system, an electric motor driveassembly would force the movable brake pad carriers 52 and 58 to carrythe slidable brake pads into their respective braking positions andslide the brake discs axially along the hub 14 into their respectivebraking positions.

[0070] The illustrative force actuator system comprises a piston andcylinder assembly operable to urge the pads 50, 54, 56 and 60 intoengagement with opposite side surfaces of the discs 38 and 40 to brakethe hub 14 and hence, the wheel. The piston and cylinder assemblycomprises a cylinder 72 which is defined by the portion 12 c of the link12. Thus, the cylinder is formed integrally with the remainder of thelink. A brake-by-wire actuator such as an electric motor could bemounted in the cylinder 72 rather than the piston 74. Herein, the piston74 of the assembly projects from the cylinder and engages the backingplate 52 on the opposite side thereof to the pad 50. The piston andcylinder assembly is operated by supplying hydraulic fluid underpressure to a bore 76 in the link portion 12 c which communicates withthe cylinder. Herein, the hydraulic pressure for operating the twin discbrake system was about 30 to 35 BAR which is one-half of the 70 BARpressure of the conventional fixed disc brake on the other test vehicle.The piston had a face of about 200 mm in area. The piston moves out ofthe cylinder moving the backing plates 52 and 58 and the discs 38 and 40until the disc 40 engages the pad 60, which does not move.

[0071] The hydraulic piston and cylinder assembly 75 includes a seal 79(FIG. 18) which acts between the cylinder 72 and the piston 74 toprevent egress of hydraulic fluid from the cylinder. This seal isprovided by an elastomeric sealing ring 81 (FIG. 18), which is mountedin an annular groove 83 formed in a cylinder wall 72 a, the ringprojecting from the groove to engage the piston. This sealing ring 81also serves as an energy storing mechanism. Specifically, when theassembly is operated to move the piston outwardly of the cylinder to putthe brake “on”, the ring is compressed thereby storing energy therein.When the pressure of the hydraulic fluid in the cylinder is reduced, thering releases the stored energy therein by moving the piston inwardly ofthe cylinder (away from the brake disc). Accordingly, the sealing ringhas to engage the piston with a significant force. Movement of thepiston away from the disc allows the movable pads 50, 54 and 56 of thebrake to be moved away from the disc by forces exerted thereon by therotating slidable brake discs 38 and 40 overcoming the force of thespring 71 a and 71 b; thereby putting the brake into a “brakes-off”condition.

[0072] The return of the piston 74 by the seal 81 reduces the off-braketorque because there is no significant force being applied by the pistonto the brake carrier 52 and its brake shoe 50 relative to the facingside of the slidable brake disc 38. Conversely, the floating brake discs38 and 40 are constrained and float on the hub 14 and will not shift thepiston inwardly into the cylinder to displace hydraulic fluid, in thecylinder causing “knock-back” during cornering or other dynamicmovements of the wheel assembly. The reduction of knock-back provides abetter feel to applying the brakes with less fluid displacement, andeliminates the occasional long pedal displacement feel where substantialfall-back has occurred.

[0073] From the foregoing, it will be seen that the present inventionprovides a much smaller disc brake assembly without the very largecaliper sliding and bolts as in the conventional, fixed disc brake. Thecaliper is large because it carries the cylinder and piston and theslidable bridge must withstand and transfer the large torque brakeloads. The present invention is smaller because the cylinder can beintegrated with the support and the bridge does not slide and carry thepiston. Because of knock back and other problems, this large fixed brakeis usually mounted at about 3:00 or 9:00 o'clock positions whereas inthe present invention the brake is mounted at the top of the unit at the12:00 o'clock position. The stiffness problem of the bridge with itsdeflection, e.g., 0.006 inch, is reduced by a factor of four when usingfour brake pads and one-half the hydraulic line pressure allowing asmaller and lighter weight brake assembly. The time of mounting andassembly of the brake, as well as repair or replacement, is enhancedbecause of the front bolting and the telescopic sliding of the brakediscs and of the brake components versus the bolt from the rear orbehind of the fixed brake bolts on which the caliper slides.

[0074]FIG. 12 is similar to FIG. 16 but illustrates a variation 100 ofthe illustrative assembly 10 in which like parts to those of theassembly 10 are given the same reference numerals and are not furtherdescribed. The assembly 100 differs from the assembly 10 in that,instead of the cylinder 72, the portion 12 c of the link 12 has twoparallel cylinders 102 formed therein. In this case, each of thecylinders 102 has a smaller transverse cross-sectional area than thecylinder 72, but the total area of the cylinders 102 is greater. Each ofthe cylinders 102 has a piston 104 therein and the pistons 104 cooperatein pressing the backing plate 52. In order to accommodate the two pistonand cylinder assemblies, the guide member 64 is modified to arch overthe pistons, as shown at 106 and the bolts 66 are replaced by threebolts 108. The use of two piston and cylinder assemblies enables greaterforce to be applied for the same pressure in the cylinders (or the sameforce to be applied for lower pressure) and this force can, on average,be applied at a greater distance from the axis 22. If desired, the twocylinders can be of different diameters, e.g., with the leading cylinderin the normal direction of rotation, being of greater diameter.

What is claimed is:
 1. A disc brake system comprising a hub beingmounted for rotation about a central axis through the hub; at least onebrake disc having an inner portion slidably mounted on the hub forsliding in a direction parallel to the central axis of the hub between abraking position and off-brake position; a drive connection between thehub and the brake disc to rotate the disc with rotation of the hub andto decelerate the rotation of the hub when the disc is in the brakingposition; braking pads including at least one slidable brake pad eachhaving a friction pad surface for applying braking torque to oppositesides of the brake disc when in the braking torque position todecelerate the engaged brake disc and thereby the hub; a stationarysupport mounting the slidable brake pad for travel between an off-brakeposition and the braking position; an actuator for sliding the slidablebrake pad and brake disc into the braking position; a disc forceapplicator applying a radially directed force between the hub and theinner portion of the brake disc to cause friction between the hub anddisc inner portion to retard their sliding axially relative to oneanother; an outer rim portion on the braking disc rotating while in theoff-brake position and engaging the slidable brake pad's frictionsurface to slide the pad from the braking position to an off-brake padposition; the slidable brake disc floating on the disc force applicatorand slidable axially along the hub from a braking position to anoff-braking position relative to the braking pads; and a brake pad forceapplicator acting on the slidable brake pad, when its off-brakeposition, to constrain the friction pad surface engaging the brake discto reduce tilting of the brake pad on the stationary support and itsrubbing on the brake disc that would increase off-brake, residualtorque.
 2. A disc brake system in accordance with claim 1 wherein thebrake pad force applicator applies force to the slidable brake pad tohold its face in a plane substantially parallel to the plane in whichthe disc is rotating to minimize tilting of the brake pad intoengagement with the brake disc, which would cause disc thicknessvariation.
 3. A disc brake system in accordance with claim 2 wherein thebrake pad force applicator comprises at least one spring pushing on thebrake pads in a direction substantially normal to the rotational axis ofthe brake disc and normal to the path of travel of the brake pads alongthe stationary support.
 4. A disc brake system in accordance with claim3 wherein the stationary support comprises a bridge; the slidable brakepad comprises a slidable pad carrier mounted for sliding on the bridgeand carrying the frictional pad surface thereon; and the spring ispositioned over the brake pad carrier and forces the brake pad carrierdownwardly against the bridge.
 5. A disc brake system in accordance withclaim 1 wherein two or more brake discs are slidably mounted on the hub;a central slidable brake pad having opposed friction pads thereon isdisposed between the twin brake discs and is slidably mounted on thestationary support; and the force applicator comprises at least onespring to constrain the slidable brake pad and the central slidablebrake pad and to assist in constraining the rims of the slidable twindisc brakes in their off-brake position.
 6. A disc brake system inaccordance with claim 1 wherein in the off-brake position, the discforce applicator holds the brake disc in a first radial plane; and thebrake pad force applicator holds its friction pad surface in a secondradial plane parallel to the first radial plane to limit contact betweenthe friction surface and brake pad to cause random kind of contacttherebetween.
 7. A disc brake system in accordance with claim 1 or claim6 wherein the brake pad force applicator comprises resilient meansforcing the brake pads against the support to provide predeterminedfrictional forces therebetween sufficient to assist in positioning theouter rims of the brake discs in an axial direction and position on thehub.
 8. A disc brake system in accordance with claim 1 wherein the forceapplicator comprises a hydraulic cylinder and a reciprocal hydraulicpiston in the cylinder; and a compressible seal ring in the cylindercompressible by the piston movement and storing energy to provide areturn force to retract the piston thereby permitting the brake pad toshift axially along its stationary support toward the cylinder duringrotation of the brake disc in its off-brake position.
 9. A disc brakesystem in accordance with claim 1 wherein the drive connection betweenthe disc and hub comprises intermeshed teeth.
 10. A disc brake inaccordance with claim 1 wherein the brake pad force applicator is alsooperable, when the slidable brake pad is in its off-brake position, toprevent the slidable brake pad from contacting the disc by slidingaxially on the stationary support.
 11. A disc brake system in accordancewith claim 9 wherein the teeth on the brake disc are provided withstress relief fillets at the junctures of the teeth to the remainder ofthe brake disc.
 12. A disc brake system in accordance with claim 1wherein: the disc expands at higher temperatures and tends to slideaxially relative to the hub; and the disc force applicator between thebrake disc and hub comprises a spring applying friction forces forlimiting the sliding of the expanded disc on the hub.
 13. A disc brakesystem in accordance with claim 5 wherein the brake pad force applicatorcomprises separate springs each engageable with the slidable frictionpad and the central slidable friction pad.
 14. A disc brake system inaccordance with claim 1 wherein the residual, off-load torque allows thebrake discs to cool quickly to less than 20 degrees above an ambienttemperature in the range of 10° to 20° C. due to residual, off-braketorque.
 15. A disc brake system in accordance with claim 1 wherein: thestationary support has a machined, supporting surface thereon; and thebrake pad comprises a slidable carrier mounted on the stationary supportand having machined slide surface thereon in sliding frictional contactwith the machined, supporting surface on the stationary support; and thebrake pad force applicator comprises a leaf spring positioned over theslidable carrier and pushing the carrier's machined slide surfaceagainst the stationary machined supporting surface to prevent tilting ofthe slidable carrier on the stationary support during the off-brakecondition.
 16. A disc brake system in accordance with claim 1 whereinthe force applicators hold the brake pad and the brake disc in parallelplanes normal to the rotation axis so that engagement of the disc withthe pad with revolution of the pad is random and avoids rubbing at thesame spot with each revolution as would cause wear and disc thicknessvariations.
 17. A disc brake system comprising a hub being mounted forrotation about a central axis through the hub; at least one brake dischaving an inner portion slidably mounted on the hub for sliding in adirection parallel to the central axis of the hub between a brakingposition and off-brake position; a drive connection between the hub andthe brake disc to rotate the disc with rotation of the hub and todecelerate the rotation of the hub when the disc is in the brakingposition; braking pads arranged on opposite sides of the disc and eachhaving a friction pad surface for applying braking torque to the discwhen in a braking position thereof, the braking pads including aslidable brake pad and a stationary brake pad which is fixed relative tothe hub; a stationary support mounting the slidable brake pad for travelbetween an off-brake position and the braking position; an actuatoroperable to slide the slidable brake pad and disc into a brakingcondition, the actuator also being operable to create sufficientclearance to allow the slidable brake pad and disc to slide into anoff-brake condition; a disc force applicator applying a radiallydirected force between the hub and the inner portion of the brake discto cause friction between the hub and disc inner portion to retard theirsliding axially relative to one another; an outer rim portion on thebraking disc rotating while in the off-brake position and engaging theslidable brake pad's friction surface to slide the pad from the brakingposition to an off-brake pad position; the slidable brake disc floatingon the disc force applicator and slidable axially along the hub from abraking position to an off-braking position relative to the brakingpads; and a brake pad force applicator acting on the slidable brake padwherein the forces applied to the disc by the disc force applicator andto the slidable brake pad by the brake pad force applicator are balancedso that the system can move from its braking condition to its off-brakecondition by the action of separation forces between the disc and thebraking pads, the disc sliding axially on the hub by a first distance tothereby separate itself from the stationary brake; and the slidablebrake pad sliding on the stationary support by a second distance, whichis greater than said first distance, to thereby separate itself from thedisc, the forces applied by the applicators in the off-brake conditionbeing sufficient to prevent axial sliding of the disc causing contactwith either braking pad, and to prevent axial sliding of the slidablepad from causing contact between the disc and the slidable pad.
 18. Adisc brake system in accordance with claim 17 wherein the disc forceapplicator forces the pads against the stationary support with forcesufficient to prevent tilting of the slidable pad on the stationarysupport from causing contact between the slidable pad and the disc. 19.A disc brake system in accordance with claim 17, including: first andsecond discs; a central slidable pad; the forces being applied to thediscs by the disc force applicator and to the slidable brake pads by thebrake pad force applicator are balanced so that the system can move fromits braking condition to its off-brake condition by the action ofseparation forces between the discs and the braking pads, the first discsliding axially on the hub by a first distance to thereby separateitself from the stationary brake pad, the central slidable brake padassembly sliding on the stationary support by a second distance, whichis greater than said first distance, to thereby separate itself from thefirst disc, the second disc sliding axially on the hub by a thirddistance, which is greater than said second distance, to therebyseparate itself from the central slidable brake pad, and the otherslidable brake pad sliding on the stationary support by a fourthdistance, which is greater than said third distance, to thereby separateitself from the second disc, the forces applied by the applicators inthe off-brake condition being sufficient to prevent axial sliding of thediscs causing contact of either disc with any of the braking pads, andto prevent axial sliding of the slidable pads from causing contactbetween either disc and either slidable pad.
 20. A disc brake system inaccordance with claim 19 wherein: the pad force applicator comprises atleast one leaf spring pushing the sliding brake pads against thestationary support; and the disc force applicator comprises at least oneleaf spring disposed between the hub and the slidable brake discs.
 21. Adisc brake system in accordance with claim 20 wherein: the leaf springof the pad force applicator comprises separate leaf springs pushingagainst the respective slidable brake pads; and the disc forceapplicator comprises a separate leaf spring disposed between each of thefirst and second brake discs.
 22. A disc brake system comprising a hubbeing mounted for rotation about a central axis through the hub; firstand second brake discs each having an inner portion slidably mounted onthe hub for sliding in a direction parallel to the central axis of thehub between a braking position and off-brake position; a driveconnection between the hub and the brake discs to rotate the discs withrotation of the hub and to decelerate the rotation of the hub when thediscs are in the braking position; braking pads each having a frictionpad surface for applying braking torque to the disc when in a brakingposition thereof, the braking pads including a slidable brake pad, acentral slidable brake pad between the first and second brake discs, anda stationary brake pad which is fixed relation to the hub; a stationarysupport mounting the slidable brake pads for travel between an off-brakeposition and the braking position; an actuator for sliding the slidablebrake pads and brake discs into the braking position; a disc forceapplicator applying a radially directed force between the hub and theinner portion of the brake disc to cause friction between the hub anddisc inner portion to retard their sliding axially relative to oneanother; an outer rim portion on each braking disc rotating while in theoff-brake position and engaging the slidable brake pad's frictionsurface to slide the pad from the braking position to an off-brake padposition; the slidable brake disc being movable axially along the hubfrom a braking position to an off-braking position relative to thebraking pads; and a brake pad force applicator acting on the slidablebrake pads wherein the forces applied to the discs by the disc forceapplicator and to the slidable brake pads by the brake pad forceapplicator are balanced so that the system can move from its brakingcondition to its off-brake condition by the action of separation forcesbetween the discs and the braking pads, the first disc sliding axiallyon the hub by a first distance to thereby separate itself from thestationary brake pad, the central slidable brake pad assembly sliding onthe stationary support by a second distance, which is greater than saidfirst distance, to thereby separate itself from the first disc, thesecond disc sliding axially on the hub by a third distance, which isgreater than said second distance, to thereby separate itself from thecentral slidable brake pad assembly, and the other slidable brake padsliding on the stationary support by a fourth distance, which is greaterthan said third distance, to thereby separate itself from the seconddisc, the forces applied by the applicators in the off-brake conditionbeing sufficient to prevent axial sliding of the discs causing contactof either disc with any of the braking pads, and to prevent axialsliding of the slidable pads from causing contact between either discand either slidable pad.
 23. A disc brake system in accordance withclaim 22 wherein: slide supporting surfaces are provided on thestationary support; the slidable brake pads have pad carriers carryingthe pad friction surfaces thereon; spaced friction slide surfaces areprovided on the pad carriers; and the pad force applicator comprises atleast one leaf spring attached to the stationary support and pushing thefriction slide surfaces against the slide supporting surfaces on thestationary support.
 24. A disc brake system in accordance with claim 23wherein a plurality of leaf springs are positioned between the hub andthe inner portion of each brake disc to increase friction between theengaged surfaces of the drive connection of the hub and disc.
 25. Avehicle braking and suspension system comprising: a vehicle suspensionhaving a suspension member; a wheel adapted to be carried by the vehiclesuspension member; a disc brake and wheel support assembly having asupporting suspension member; a rotatable hub mounted on the suspensionmember for rotation about a central rotational axis through the hub andcarrying the wheel for rotation about the rotational axis; a brakeactuator for the disc brake mounted on the supporting suspension member;a stationary bridge on the suspension member and having slidablesurfaces thereon; at least one brake disc mounted on the hub for brakingthe hub and wheel; an outer, fixed brake pad mounted on the bridge forengaging one side of the brake disc; a slidable brake pad mounted on theslidable surfaces of the stationary bridge and slidable by the brakeactuator to engage a friction surface thereon with the other side of thedisc and to slide the brake disc axially along to the hub from anoff-brake, residual torque position to a on-brake position in which thebraking pads are engaging opposite sides of the brake disc to brake thedisc, hub and wheel; and a brake pad force applicator carried on thestationary bridge applying force to the brake pad to hold the brake padin a plane parallel to the plane of the slidable brake disc.
 26. Avehicle braking system in accordance with claim 25 wherein the brake padforce applicator comprises a resilient spring member mounted on thestationary bridge.
 27. A vehicle braking system in accordance with claim25 wherein sliding surfaces on the stationary bridge have slidingfrictional engagement with sliding surfaces on the brake disc; and thebrake pad force applicator comprises a resilient spring member mountedto overlie the brake pad and to apply a predetermined spring force tothe brake pad to increase substantially the friction beyond that neededto prevent rattling of the brake pad on the bridge.
 28. A vehiclebraking system in accordance with claim 25 wherein the brake actuatorfor the disc brake comprises a hydraulic cylinder having a piston forforcing the slidable brake pad into the braking position; a compressibleseal ring between the cylinder and piston exerts a return force on thepiston when the braking fluid pressure is relieved at the no-loadbraking position; and the hydraulic cylinder being mounted at an uppervertical position on the suspension.
 29. A vehicle braking system inaccordance with claim 25 wherein: a second brake disc is mounted on thehub for axial sliding movement thereon; and a central brake pad carrierhaving opposed friction pads is slidably mounted on the stationarybridge to engage facing sides of the respective brake discs; the forceapplicator holding the central pad carrier in an off-brake, residualtorque position relative to the rotating brake discs.
 30. A vehiclebraking system in accordance with claim 25 wherein a friction forceapplicator is positioned between the brake disc and the hub to exertfriction forces to assist the brake pads in positioning the brake discsat off-brake, residual load positions
 31. A vehicle braking system inaccordance with claim 25 wherein intermeshed splines are formed on thebrake disc and the hub to provide a positive drive connectiontherebetween; and spring members are positioned between the hub and thebrake disc to apply frictional forces to resist free sliding of thebrake disc on the hub as the brake disc is heated and expands andthereafter contracts when cooled.
 32. A vehicle braking system inaccordance with claim 25 wherein the two brake discs cool to less than20° C. above ambient temperature when the ambient temperature is in therange of 10° C. to 20° C.
 33. A vehicle braking system in accordancewith claim 25 wherein the rotating brake disc and the brake pads and thebrake pad force applicators position the brake discs for randomlyengaging the brake pads at different locations, thereby preventing weardue to engagement at the same spot on the disc during each revolution aswould cause disc thickness variation.
 34. A method of disc brakingemploying inner and outer, annular brake discs mounted on a rotatablehub for axial sliding thereon and having a fixed caliper bridge withfour brake pad frictional surfaces thereon for engaging opposite sidesof the brake discs, said method comprising: applying an actuating forceon the slidable brake pads to slide them along the bridge to a brakingposition to engage rims of the annular discs with the four padfrictional surfaces to generate braking forces to decelerate the discs;pushing the brake discs by the slidable brake pads along the hub toengage an outer side of an outer brake disc with a stationary brake padon the fixed bridge at the braking position; relieving the actuatingforce after braking; exerting forces by the rotating brake discs on theslidable brake pads to overcome predetermined spring forces holding theslidable brake pads against sliding to shift the brake pads to off-brakepositions; exerting spring forces between each of the brake discs andhub to assist in locating the brake discs on the hub at off-brakepositions; and limiting engagement between the rotating brake discs andthe brake pads at their respective off-brake positions to only randomengagement therebetween to minimize disc thickness variation due torubbing and to minimize off-load, residual torque between the discs andbrake pads.
 35. A method in accordance with claim 34 including theproviding of the disc brake assembly on a vehicle suspension; andmaintaining the temperature of the brake discs due to off-brake residualtorque to less than 20° above ambient temperature when the ambienttemperature is in the range of 10° to 20° C. as the vehicle is beingdriven in a straight line path.
 36. A method in accordance with claim 34including the providing of the disc brake on a vehicle suspension; anddriving the vehicle through the AMS test and maintaining the temperatureof the brake discs below 650° C.
 37. A method in accordance with claim36 including the step of maintaining the brake disc temperature below600° C.
 38. A method in accordance with claim 34 actuating the brakepads from a position above the rotational axis through the hub and in avertical plane at a substantial 12:00 o'clock position.
 39. A method inaccordance with claim 34 wherein the applying of the actuating force onthe slidable brake pads comprises moving a hydraulically operated pistonto force at least two slidable brake pads and at least two slidablebrake discs to shift to the braking position.
 40. A method in accordancewith claim 34 including holding the brake pads against tilting on thesupporting bridge to prevent localized rubbing and resultant discthickness variation while the braking system is experiencing vibrationand vehicle inertial forces.
 41. A method in accordance with claim 34including the step of balancing the spring forces on the brake pads andbrake discs to allow separation from one another to shift into anoff-brake position and to hold them against tilting to prevent discthickness variation of the brake discs.
 42. A vehicle, front wheelbraking assembly comprising: a suspension support casting; a rotatablehub journaled in the suspension support casting for rotation about asubstantially horizontal axis of rotation; inner and outer slidablebrake discs slidably mounted on the hub and each having aninterconnection with the hub to rotate with the hub; a fixed bridge onthe suspension supporting casting having slidable support surfacesthereon and having a distal end; a fixed brake pad mounted on the distalend of the fixed bridge to engage an outer face of the outer slidablebrake disc; a central brake pad carrier carrying a pair of opposed brakepad surfaces to engage facing sides of the inner and outer brake discsmounted on the slidable support surfaces of the fixed bridge; an innerbrake pad carrier having an inner brake pad surface mounted on theslidable surfaces of the fixed bridge; an integral, hub support portionof the suspension support casting mounting the hub and attached wheelfor rotation about the rotational axis; a substantially vertical bore inthe suspension support casting to receive a ball joint to permit thesuspension support casting to turn about an axis therein; an integralconnecting portion on the suspension support casting for connection to asteering system to turn the suspension support casting about a swivelaxis; and an integral actuator bore in a top portion of the suspensionsupport casting located above the rotational axis and in a vertical,substantially 12:00 o'clock position with the bridge and brake padcarriers also being at the substantially 12:00 o'clock position forengaging the upper outer rim portions of the slidable discs.
 43. Avertical braking assembly in accordance with claim 42 wherein theintegral actuator bore comprises a hydraulic cylinder bore; and a pistonis mounted in the integral hydraulic cylinder bore.
 44. A vehiclebraking assembly in accordance with claim 42 wherein a brake-by-wireactuator is mounted in the integral actuator bore.
 45. A vehicle brakingassembly in accordance with claim 42 wherein the integral supportcasting comprises a connecting portion for connection to a McPhersonstrut so that the integral suspension casting can pivot about an axis ofthe strut.